%!TEX root = ./HDG_report.tex
\section{Game relevance}\label{gamedesign}

So far, we have only introduced our conceptual model, which is simply a way to describe a sound using two components: a \emph{source sound} and a \emph{sound descriptor}. While we are not providing any general algorithm for generating either a source sound or a sound descriptor, we believe that this concept in itself holds very high relevance to games. Having access to a variety of sounds using a single source could greatly reduce the amount of hard drive space a game would take. Also, and probably most interestingly, this technique could provide a very accessible way of interfacing with other forms of procedurally generated content in games. In the case of Galactic Arms Race (GAR) \cite{stanley2009gar}, for example, the sound descriptor could be a function of the weapon's evolved CPPR, providing each weapon with its own unique sound.

\subsection{The HDGrains demo}

We have created a small game where the player battles against a computer player in space. The game consists of two screens: the weapon select screen and the battle screen. In the weapon select screen, the player can preview the sound of one weapon chosen for the enemy as well as several choices of a weapon for himself. After listening to the sound of the enemy's weapon, the player must choose one of five possible weapons before proceeding to the battle screen. In the battle screen, the actual fight is carried out, and this is where the player will be able to see the chosen weapon in action. Each player is assigned one half of the screen to move around in. For each weapon there are four generated envelopes \footnote{In audio terminology, an envelope is any form of curve} that determine both the behavior of the weapon, and the structure of the sound descriptor. Because of this, a sound will in theory describe a weapon completely (and vice versa). 

A weapon can be one of three different elements: fire, ice, lightning. The relation between these is the same as in rock-paper-scissors -- every element is weak against exactly one other element. Fire is weak against lightning, lightning is weak against ice and ice is weak against fire. Similar to GAR, particles cancel each other out on collision. However, if the particles are of different elements, only the weaker element particle will be canceled. The player that possesses the stronger element will therefore have a great advantage, as that player can both break through the opponent's shots as well as defend against incoming attacks. A weapons trajectory and speed will also have a big impact on it's effectiveness, so wielding the superior element will not necessarily result in victory. 

Both players have a health bar that also functions as weapon energy. Health is lost whenever a player is hit by an enemy particle and the player will be defeated once the health reaches 0\%. Firing the weapon will also decrease health with a reduction amount determined from the duration of the shot. When health reaches 1\%, firing the weapon will no longer decrease health. Health will begin recharging after a short while if the player avoids damage and refrains from firing the weapon. This health system forces the player to plan when to shoot and when to focus on dodging. Continuously firing the weapon will ultimately leave the player very vulnerable to attacks from the opponent.

While the concept of generating sound is interesting in itself, we hope to illustrate something more with this game. As previously mentioned, using GAR as an example, we could provide any generated content with unique sounds. Still, in this case, the audio would ultimately fill its traditional role as aesthetic flavor in the game. If the player decided to mute the audio, the gameplay would not be affected. In our game, however, we are attempting to shift the emphasis to the sound itself, as it is the only thing that guides the player's choice of weapon. The performance of the selected weapon has great significance in the context of the game, and so, an important part of the game is played in the weapon select screen, but only through listening. 

With this demo, we hope to provide a case where generated audio is pushed closer to being viewed as necessary rather than optional for the experience of the game.